Afflerbach, an Allentown Democrat running against Toomey for Congress in the 15th District, said the budget surplus -- estimated by the Congressional Budget Office to be $520 billion over the next five years -- would disappear under a flat tax, leaving nothing to preserve Social Security.

"Unfortunately, under Mr. Toomey's risky new tax scheme, the budget surplus would disappear more quickly than a beer during happy hour at one of Mr. Toomey's nightclubs," Afflerbach, a state senator, said at a news conference attended by about a dozen sign-carrying senior citizens.

The news conference coincided with the launch Tuesday of a radio advertisement in which Afflerbach, playing off the Little Red Riding Hood theme, equates Toomey to the wolf hiding under the bed.

"Like the wolf, Mr. Toomey's not what he appears to be," Afflerbach said. "We just can't trust Pat Toomey to protect Social Security."

Critics of a flat tax, which is designed to tax all income once and at the same rate, say it would cause the loss of billions of dollars in revenue.

"(Toomey's) new tax plan is estimated to saddle us with budget deficits ranging between $120 billion and $200 billion each year," Afflerbach said, citing estimates by Citizens for Tax Justice. "And that means Mr. Toomey's untested new scheme could cost Social Security another $600 billion to $1 trillion over the next five years."

Afflerbach favors using all the budget surplus to repay money taken over the years from the Social Security Trust Fund to pay for other government programs.

"There is nothing about a flat tax that creates a deficit," he said. "We can absolutely have a flat tax and balance the budget."

Toomey said the federal government is expected to generate a $700 billion surplus over the next 10 years and he favors using it to preserve Social Security.

Toomey said the Social Security budget should be separate from the general fund budget. "A flat tax has nothing to do with it, and he knows it," he said.

"Roy Afflerbach, a 16-year tax-hiker extraordinaire, wants to preserve the government's disastrous 17,000-page IRS tax code against the will of the voters because it makes it easy for him and other career politicians to stick, hide and otherwise bury all kinds of tax increases in it," Toomey said.